1. Field of the Invention
The present invention relates generally to the field of video processing and, more specifically, to efficient EWA video rendering.
2. Description of the Related Art
Visual content is presented on a broad range of displays, from large scale cinema screens, consumer flat screen monitors, and personal computer screens to various types of mobile devices. Typically, one or more aspects of the visual content are changed in order to present the content in a form that is compatible with a particular display. Because picture element (pixel) resolution, aspect ratio, and frame rate of displays vary significantly, rendering visual content from a source format into a target format is practically performed at or near the display, rather than at or near the source of the visual content. In addition, various transformations are often added to visual content, such as image rotation, image size reduction or magnification, special effects such as water-rippling effects, and the like.
Various applications benefit from rendering video from the source format to the target format using a non-linear scaling technique. With non-linear scaling, certain portions of the visual content may be rendered using one scaling factor, while other portions of the visual content are rendered using other scaling factors. With content aware video retargeting from one aspect ratio to another, visually important regions of the content are scaled linearly to retain their original aspect ratio and to avoid distortion. Visually less important regions of the content are distorted more via non-linear scaling to accommodate the visually more important regions. With stereoscopic three-dimensional (S3D) viewing, the impression of depth may be increased or decreased by non-linearly scaling certain portions of the visual content more or less, relative to other portions. The degree of non-linear scaling could be controlled, for example, by a depth control associated with the display. With multi-viewer stereoscopic displays, multiple S3D signals are delivered to the display, where each S3D signal may be created using different non-linear scaling parameters. Each viewer may select one of the multiple S3D signals for viewing based on the viewer's distance and angle with respect to the display.
Scaling may be performed via any technically feasible approach known in the art, including, without limitation, interpolation techniques, such as bilinear interpolation, Lanczos interpolation, linear interpolation, and kernel splatting, and anti-aliasing techniques, such as super-sampling, mip-mapping, and kernel splatting. One such technique uses a non-linear scaling approach for interpolation and anti-aliasing called elliptical weighted average (EWA) rendering, which is also known as EWA splatting. EWA splatting implicitly handles anti-aliasing efficiently relative to at least some other techniques. However, current EWA splatting techniques suffer from over-blurring of the visual content, causing a reduced visual experience. In addition, EWA is computationally expensive, typically using special processing units such as graphics processing units (GPU). These special processing units may be costly, large in size, and have relatively high power requirements, making current EWA splatting techniques impractical for consumer displays such as flat screen monitors and mobile devices.